The invention relates to a method and an apparatus for determining the triacetin content in filter plugs for cigarettes during the manufacture of the filter plugs from a filter tow consisting of, in particular, cellulose acetate.
Cigarette filters generally consist of cellulose acetate and contain triacetin, specifically typically in an amount of approximately 8% (m/m). The triacetin is essential for the filter action.
Currently there is no reliable possibility whatsoever for determining or even controlling the triacetin content online during filter manufacture. Therefore filter manufacturers in general resort to a laboratory method by taking filter samples with and without triacetin from the process and comparing these offline by weighing. The consequence is that in the event of the supply of triacetin stopping suddenly (for example when a container is empty, a solenoid valve becomes stuck, etc.) this is usually noticed only at the time of the next offline laboratory check. However, if a filter plug is produced without an adequate supply of triacetin, the filter action deteriorates to such an extent that the health-promoting measures of the filter are non-existent. If the damage is not noticed in good time, many millions of cigarettes which have already been produced, and frequently have already been packed, have to be broken up again and returned to production. After the tobacco, the filter material is the most expensive starting material. The filter material cannot be recycled. Considerable costs are thus incurred.
Previous attempts using other physical methods to determine the filter mass and to control the supply of triacetin have not led to success.
For instance, it is known to determine the filter mass on the plug with the aid of a radioactive beta radiation emitter and detector (DE 28 IS 025 A). However, because the degree of interaction between the lightweight mass of the filter plug and the beta radiation is too low and because of the restriction of detecting only a damping signal of the electrons, in the case of simultaneous fluctuations in the moisture content, filter tow content and triacetin content the accuracy of measurement with this method is too low to achieve a reasonable weight or triacetin control. A method developed in the 1990s for the use of infra-red absorption lines of the triacetin for triacetin determination did not result in adequate accuracies because the near infra-red absorption method, as an optical measurement procedure is only a surface measurement method and is able to penetrate only a few wavelengths, that is to say a few micrometers, into the product. Measurement of the triacetin content downstream of the cutter downstream of the filter maker and vertically to the cut edge of the filters was also not able to compensate for this fundamental defect of the IR method (instrument from cooperation between Moisture Systems, Hopkinton and Celanese, Charlotte, USA). At the same time, only a minute portion of the product is detected within the NIR measurement radiation and within the penetration depth by this means.